In a conventional screen printing machine, correction of the position of a printing screen with respect to an article to be printed (hereinafter referred to as "printed article") such as a substrate for an electronic component or the like, is carried out by means of a mechanism for concurrently adjusting three axes. This mechanism thus corrects the position of the screen in a lateral direction (X-axis correction), it corrects the position thereof in a longitudinal direction perpendicular to the lateral direction (Y-axis correction), and it corrects the position thereof in a rotational direction (.theta.-axis correction). Such a conventional position adjusting mechanism is shown in FIG. 4 by way of example. More particularly, the mechanism includes a first adjustment member 3 arranged for laterally moving a screen frame 2 mounted thereon with a screen printing mask or printing screen 1 to carry out X-axis correction of the printing screen 1, as well as second and third adjustment members 4 and 5 arranged in juxtaposition to each other for moving the screen frame 2 in a longitudinal direction to carry out Y-axis correction of the printing screen 1. The second adjustment member 4 and third adjustment member 5 are also constructed so that the amount of correction by the members 4 and 5, respectively, are different from each other in order to concurrently carry out correction of the printing screen 1 in a .theta.-axis direction.
Thus, the conventional position adjusting mechanism shown in FIG. 4 is adapted to concurrently adjust the three X-, Y- and .theta.-axes, so that adjustment of each of these axes leads to a variation in correction of the remaining axes. For example, changes in the amounts of correction of the second and third adjustment members 4 and 5 for the .theta.-axis correction will require a variation in the amount of Y-axis correction, as well as the x-axis correction. This fails to facilitate printing position correcting, resulting in the operation being troublesome and time consuming.
The present invention is an attempt to overcome the foregoing disadvantages of the prior art. Accordingly, it is an object of the present invention to provide a method and an apparatus for correcting a screen position during screen printing, which are capable of accomplishing correction of a printing position in a short period of time by independently carrying out correction of a position of a screen frame in a rotational direction, or .theta.-axis correction of the screen frame, the screen frame having a printing screen mounted thereon.
This and other objects and the novel features of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment of the invention.